Why am I having increased menstrual cycle frequency on the Implanon after 2 years?

For the first 2 years with the implant, I maybe had my period twice. Over the last 6 months I have had it about 4 times, twice within 2 weeks of each other. I'm not due to have it removed until February of 2016 but the increased frequency is making me nervous. Is there anything that could cause this?